The Reproductive System

The Reproductive System

Reproductive System Primary sex organs (gonads) – testes in males, ovaries in females Gonads produce sex cells called gametes and secrete sex hormones Accessory reproductive organs – ducts, glands, and external genitalia Sex hormones – androgens (males), and estrogens and progesterone (females)

Reproductive System Sex hormones play roles in:
The development and function of the reproductive organs Sexual behavior and drives The growth and development of many other organs and tissues Follicle stimulating hormone (FSH) - Stimulates follicle development and estrogen secretion in females and sperm production in males Leutinizing hormone (LH) - Causes ovulation and progestin production in females and androgen production in males Internal and environmental stimuli CNS Hypothalamus Anterior pituitary Steroid and peptide hormones Gamete production GnRH Short-loop negative feedback Long-loop feedback may be negative or positive Stimulus Integrating center Efferent pathway Effector Tissue response LH Endocrine cells FSH Gonads (ovaries or testes) KEY Females only

Male Reproductive System
The male gonads (testes) produce sperm and lie within the scrotum Sperm are delivered to the exterior through a system of ducts: epididymis, ductus deferens, ejaculatory duct, and the urethra Accessory sex glands: Empty their secretions into the ducts during ejaculation Include the seminal vesicles, prostate gland, and bulbourethral glands

The Scrotum Contains paired testicles that hangs outside the abdominopelvic cavity Its external positioning keeps the testes 3C lower than core body temperature (needed for sperm production) Intrascrotal temperature is kept constant by two sets of muscles: Dartos – smooth muscle that wrinkles scrotal skin Cremaster – bands of skeletal muscle that elevate the testes

The Testes Seminiferous tubules produce the sperm
Surrounding the seminiferous tubules are interstitial (Leydig) cells that produce androgens and sustentacular (Sertoli) cells that release androgen-binding proteins (ABP) Epididymis functions to mature and store sperm cells (at least 20 days) Spermatic cord – encloses PNS and SNS nerve fibers, blood vessels, and lymphatics that supply the testes

The Penis Internal penis
Urethra Conveys both urine and semen (at different times!) Three cylindrical bodies of erectile tissue Corpus spongiosum and corpora cavernosa Spongy network of connective tissue and smooth muscle riddled with vascular spaces Erection – during sexual excitement, the erectile tissue fills with blood causing the penis to enlarge and become rigid

Seminal Vesicles Secrete 60% of the volume of semen
Semen – viscous alkaline fluid containing fructose, ascorbic acid, coagulating enzyme (vesiculase), and prostaglandins Join the ductus deferens to form the ejaculatory duct where sperm and seminal fluid mix

Prostate Gland Gland that encircles part of the urethra inferior to the bladder Secretes milky fluid, which contains enzymes that assist in the activation of sperm Accounts for one-third of the semen volume

Bulbourethral Glands (Cowper’s Glands)
Pea-sized glands inferior to the prostate Produce thick, clear mucus prior to ejaculation that neutralizes traces of acidic urine in the urethra

Semen Milky white, sticky mixture of sperm and accessory gland secretions Provides a transport medium and nutrients (fructose), protects and activates sperm, and facilitates their movement Prostaglandins in semen: Decrease the viscosity of mucus in the cervix Stimulate reverse peristalsis in the uterus, facilitates movement through female reproductive tract Suppress immune response

Semen The hormone relaxin enhances sperm motility
The relative alkalinity of semen neutralizes the acid environment found in the male urethra and female vagina Seminalplasmin – antibiotic chemical that destroys certain bacteria Clotting factors coagulate semen immediately after ejaculation, then fibrinolysin liquefies the sticky mass Only 2-5 ml of semen are ejaculated, but it contains million sperm/ml

Male Sexual Response Erection is initiated by sexual stimuli including: Touch and mechanical stimulation of the penis Erotic sights, sounds, and smells Erection can be induced or inhibited solely by emotional or higher mental activity Impotence – inability to attain erection Erotic stimuli Higher brain centers Descending autonomic pathways Ascending sensory pathway Sensory neuron Mechanoreceptor Erection Penile arterioles vasodilate. Thoughts of Sex!! Parasympathetic stimulated Sympathetic inhibited Tactile Spinal cord Stimulus Receptor Afferent pathway Integrating center Efferent pathway Effector Tissue response KEY Penis

Male Sexual Response: Erection
Enlargement and stiffening of the penis from engorgement of erectile tissue with blood During sexual arousal, a parasympathetic reflex promotes the release of nitric oxide Nitric oxide causes erectile tissue to fill with blood Expansion of the corpora cavernosa: Compresses the drainage veins Retards blood outflow and maintains engorgement The corpus spongiosum functions in keeping the urethra open during ejaculation Erotic stimuli Higher brain centers Descending autonomic pathways Ascending sensory pathway Sensory neuron Mechanoreceptor Erection Penile arterioles vasodilate. Thoughts of Sex!! Parasympathetic stimulated Sympathetic inhibited Tactile Spinal cord Stimulus Receptor Afferent pathway Integrating center Efferent pathway Effector Tissue response KEY Penis

Ejaculation The propulsion of semen from the male duct system
At ejaculation, sympathetic nerves serving the genital organs cause: Reproductive ducts and accessory organs to contract and empty their contents Bladder sphincter muscle to constrict, preventing the expulsion of urine Epididymis, seminal vesicles, prostate gland and bulbospongiosus muscles rhythmically contract, propelling the semen (about 3-5 ml) through the urethra

Sperm Conveyance From seminiferous tubules, the sperm enter the epididymis Upon ejaculation the epididymis contracts, expelling sperm into the ductus deferens Ductus deferens merges with the duct of the seminal vesicle form the ejaculatory duct From ejaculatory duct, sperm enter urethra Vasectomy – cutting and ligating the ductus deferens, which is a nearly 100% effective form of birth control

Spermatogenesis The sequence of events that produces sperm in the seminiferous tubules of the testes 400 million sperm formed per day Each cell has two sets of chromosomes (one maternal, one paternal) and is said to be diploid (2n chromosomal number) Humans have 23 pairs of homologous chromosomes Gametes only have 23 chromosomes and are said to be haploid (n chromosomal number) Gamete formation is by meiosis, in which the number of chromosomes is halved (from 2n to n)

Comparison of Mitosis and Meiosis
Figure 27.6

Spermatogenesis: Sperm Production in the Testis

Spermatogenesis Cells making up the walls of seminiferous tubules are in various stages of cell division These spermatogenic cells give rise to sperm in a series of events Mitosis of spermatogonia, forming spermatocytes Meiosis forms spermatids from spermatocytes Spermiogenesis – spermatids form sperm

Mitosis of Spermatogonia
Spermatogonia – outermost cells in contact with the epithelial basal lamina Spermatogenesis begins at puberty as each mitotic division of spermatogonia results in type A or type B daughter cells Type A cells remain at the basement membrane and maintain the germ line Type B cells move toward the lumen and become primary spermatocytes

Spermatocytes to Spermatids
Primary spermatocytes undergo meiosis I, forming two haploid cells called secondary spermatocytes Secondary spermatocytes undergo meiosis II and their daughter cells are called spermatids Spermatids are small round cells seen close to the lumen of the tubule

Spermiogenesis: Spermatids to Sperm
Late in spermatogenesis, spermatids are nonmotile Spermiogenesis – spermatids lose excess cytoplasm and form a tail, becoming motile sperm Sperm have three major regions Head – contains DNA and hydrolytic enzymes that allow the sperm to penetrate and enter the egg Midpiece – contains mitochondria spiraled around filaments Tail – a typical flagellum produced by a centriole

Spermatogenesis Figure 27.8b, c

Regulation of Spermatogenesis
Spermatogenesis and testicular androgen production involve the hypothalamus, anterior pituitary gland, and the testes Testicular regulation involves 3 sets of hormones: GnRH stimulates the testes to produce the gonadotropins FSH and LH FSH and LH stimulate the cells of the testes to produce testosterone and ABP Testosterone and inhibin also exert negative feedback controls LH GnRH Hypothalamus Anterior pituitary Inhibin Testes Leydig cells Testosterone (T) To body for secondary effects FSH Integrating center Efferent pathway Effector Tissue response Sertoli cell Cell products Second messenger ABP T Androgen-binding protein (ABP) Spermatogonium Spermatocyte KEY

Hormonal Regulation of Testes
The hypothalamus releases gonadotropin-releasing hormone (GnRH) GnRH stimulates the anterior pituitary to secrete FSH and LH FSH causes sustentacular (Sertoli) cells to release androgen-binding protein (ABP) LH stimulates interstitial (Leydig) cells to release testosterone ABP binding of testosterone enhances spermatogenesis Feedback inhibition on the hypothalamus and pituitary results from rising levels of testosterone and increased production of inhibin

Effects of Testosterone Activity
Testosterone is synthesized from cholesterol Testosterone is necessary for fetal development of male external genitalia Increased levels of testosterone at puberty are responsible for further growth of male genitalia and for the development and maintenance of male secondary sex characteristics Testosterone also stimulates protein synthesis and accounts for the greater muscular development of the male

Male Secondary Sex Characteristics
Male hormones make their appearance at puberty and induce changes in nonreproductive organs, including Appearance of pubic, axillary, and facial hair Enhanced growth of the chest and deepening of the voice Skin thickens and becomes oily Bones grow and increase in density Skeletal muscles increase in size and mass Testosterone is the basis of libido in both males and females

Part 2 Female Reproductive System

Female Reproductive System
Ovaries are the primary female reproductive organs Make female gametes (ova) Secrete female sex hormones (estrogen and progesterone) Internal genitalia – ovaries, uterine tubes, uterus, vagina External genitalia – vulva, clitoris, labia, and hymen

Ovaries Embedded in the ovary cortex are ovarian follicles
Each follicle consists of an immature egg called an oocyte

Ovaries Primordial follicle – one layer of squamous-like follicle cells surrounds the oocyte Primary follicle – two or more layers of cuboidal granulosa cells enclose the oocyte Secondary follicle > tertiary follicle – at its most mature stage bulges from the surface of the ovary (AKA vesicular or Graafian follicle) Ovulation – ejection of the oocyte from the ripening follicle Corpus luteum – ruptured follicle after ovulation

Secondary follicle Tertiary follicle OVULATION Corpus luteum Follicle
Primordial follicles before puberty Secondary follicle Tertiary follicle OVULATION Corpus luteum Follicle cells Primary oocytes Zona pellucida Nucleus of primary oocyte Zona pellucida Antrum containing follicular fluid Outer surface ovary Released secondary Corona radiata Corpus luteum Degenerating corpus Primordial follicles follicle Secondary Tertiary

Uterine Tubes (Fallopian Tubes)
Receive the ovulated oocyte and provide a site for fertilization The uterine tubes have no contact with the ovaries and the ovulated oocyte is cast into the peritoneal cavity Beating cilia on the fimbriae create currents to carry the oocyte into the uterine tube The oocyte is carried toward the uterus by peristalsis and ciliary action

Uterus Hollow, thick-walled organ
Functions of the uterus: receives, retains and nourishes the fertilized egg Three layers Perimetrium – outermost serous layer; the visceral peritoneum Myometrium – middle layer; interlacing layers of smooth muscle Endometrium – mucosal lining of the uterine cavity

Endometrium Inner layer Allows for implantation of a fertilized egg
Sloughs off if no pregnancy occurs (menses) Has numerous uterine glands that change in length as the endometrial thickness changes

Vagina Organ of copulation - receives the penis during sexual intercourse Provides a passageway for birth, menstrual flow Vaginal mucosa does not have glands, lubrication is provided by cervical mucus glands / vestibular glands pH of vagina in women is acidic Maintained by glycogen stores that are used by resident normal flora Keeps vagina healthy Low pH is hostile to sperm

Vulva Mons pubis - mound of fatty tissue overlying the pubic symphysis
Labia majora - outer folds of skin contains fat, sudoriferous and sebaceous glands, covered with pubic hair (homologous to scrotum) Labia minora - inner folds of skin containing sebaceous glands and nerve endings that provide stimulation Clitoris - cylindrical mass of erectile tissue covered by a layer of skin called the prepuce (homologous to penis) Vestibule - cleft between the labia minora includes the urethral orifice, vaginal orifice and vestibular glands that produce lubricants during sexual intercourse.

Mammary Glands Modified sweat glands consisting of lobes that radiate around and open at the nipple Lobes contain glandular alveoli that produce milk in lactating women

Lactation: Milk Secretion
Oxytocin Prolactin Inhibition of prolactin cells is removed. Oxytocin neuron Portal system PIH cell Anterior pituitary Posterior Hypothalamus PIH Ascending sensory information Sound of child’s cry Higher brain centers Milk secretion Mechanoreceptors in nipple Baby suckling Smooth muscle contraction ejected The hormonal control of milk secretion and release Prolactin - milk production Prolactin-inhibiting hormone (PIH) Suckling - inhibits PIH Oxytocin – milk “expressed”

Overview

Oogenesis Production of female sex cells by meiosis
During fetal period Oogonia (diploid ovarian stem cells) multiply by mitosis and store nutrients Primordial follicles appear as oogonia are transformed into primary oocytes Primary oocytes begin meiosis but stall in prophase I

Oogenesis During childhood ovaries inactive From puberty
Each month one activated primary oocyte completes meiosis one to produce two haploid cells The first polar body The secondary oocyte The secondary oocyte arrests in metaphase II and is ovulated If penetrated by sperm the second oocyte completes meiosis II, yielding: One large ovum (the functional gamete) A tiny second polar body

Ovarian Cycle Monthly series of events associated with the maturation of an egg Follicular phase – period of follicle growth (days 1–14) Ovulation occurs mid-cycle Luteal phase – period of corpus luteum activity (days 14–28)

Follicular Phase The primordial follicle, directed by the oocyte, becomes a primary follicle Primary follicle becomes a secondary follicle - thecal and granulosa cells produce estrogens The secondary follicle becomes a vesicular follicle (Graafian follicle)

Ovulation Ovulation occurs during a surge of LH levels
Ovary wall ruptures and expels the secondary oocyte 1-2% of ovulations release more than one secondary oocyte, which if fertilized, results in fraternal twins

Luteal Phase After ovulation, the ruptured follicle collapses, granulosa cells enlarge, and along with internal thecal cells, forms the corpus luteum The corpus luteum secretes progesterone and estrogen If pregnancy does not occur, the corpus luteum degenerates in 10 days, leaving a scar (corpus albicans) If pregnancy does occur, the corpus luteum produces hormones until the placenta takes over that role (at about 3 months)

Luteal phase and Late Luteal phase
Figure 26-14c, d: Hormonal control of the menstrual cycle

Establishing the Ovarian Cycle
During childhood, ovaries grow and secrete small amounts of estrogen that inhibit the hypothalamic release of GnRH As puberty nears, GnRH is released; FSH and LH are released by the pituitary, which act on the ovaries These events continue until an adult cyclic pattern is achieved and menarche occurs

Hormonal Interactions of Ovarian Cycle
LH FSH GnRH Androgens Estrogens Follicle Granulosa cells Thecal Corpus luteum Progesterone Ovum Stimulus Integrating center Efferent pathway Tissue response Early to mid-follicular phase Estrogen Inhibin KEY Pituitary Hypothalamus (a) Day 1 – GnRH stimulates the release of FSH and LH FSH and LH stimulate follicle growth and maturation, and low-level estrogen release Rising estrogen levels initially: Inhibit the release of FSH, LH, GnRH Gonadotropins accumulate in pituitary Positive feedback on granulosa cells produce more estrogen

LH FSH GnRH Androgens Estrogens Follicle Granulosa cells Thecal Corpus luteum Progesterone Ovum Early to mid-follicular phase Late follicular phase and ovulation Estrogen Inhibin High estrogen output Small amount of progesterone Pituitary Hypothalamus (a) (b) Further increase in estrogen levels have a positive feedback effect on the pituitary, causing a sudden surge of LH The LH spike stimulates the primary oocyte to complete meiosis I, and the secondary oocyte continues on to metaphase II

FSH LH New follicles begin to develop Corpus luteum dies Tonic secretion resumes Corpus luteum Progesterone Ovum Follicle Estrogen and progesterone Stimulus Integrating center Efferent pathway Tissue response (from ovulated follicle) Estrogen Inhibin GnRH secretes Late follicular phase and ovulation Late luteal phase Early to mid-luteal phase Granulosa cells Thecal High estrogen output Small amount of Androgens KEY (b) (d) (c) Day 14 – LH triggers ovulation LH transforms the ruptured follicle into a corpus luteum, which produces inhibin, progesterone, and estrogen - shuts off FSH and LH release and declining LH ends luteal activity Days – decline of the ovarian hormones, ends the blockade of FSH and LH, cycle starts anew

Uterine (Menstrual) Cycle
Series of cyclic changes that the uterine endometrium goes through each month in response to ovarian hormones in the blood Days 1-5: Menstrual phase (menses) Degeneration of the endometrium Uterus sheds all but the deepest part of the endometrium Days 6-14: Proliferative (preovulatory) phase – Restoration of the endometrium Days 15-28: Secretory (postovulatory) phase Endometrial glands enlarge and accelerate their rates of secretion Endometrium prepares for implantation of the embryo

Menses If fertilization does not occur, progesterone levels fall, depriving the endometrium of hormonal support Spiral arteries kink and go into spasms and endometrial cells begin to die The functional layer begins to digest itself Spiral arteries constrict one final time then suddenly relax and open wide The rush of blood fragments weakened capillary beds and the functional layer sloughs

The Menstrual and Uterine Cycles
Follicular Phase Luteal Phase Phases of the Uterine Cycle Primary follicle Theca Ovulation Corpus luteum formation Mature corpus Ovarian Cycle Basal body temperature (˚C) Uterine cycle Ovarian hormone levels Gonadotrophic MENSES PROLIFERATIVE PHASE SECRETORY PHASE Inhibin Estrogen Antrum FSH 36.4 36.7 DAYS 28/0 7 14 21 albicans LH Progesterone

Extrauterine Effects of Estrogens and Progesterone
Estrogen levels rise during puberty Promote oogenesis and follicle growth in the ovary Exert anabolic effects on the female reproductive tract Uterine tubes, uterus, and vagina grow larger and become functional Uterine tubes and uterus exhibit enhanced motility Vaginal mucosa thickens and external genitalia mature

Extrauterine Effects of Estrogens and Progesterone
Growth of the breasts Increased deposition of subcutaneous fat, especially in the hips and breasts Widening and lightening of the pelvis Growth of axillary and pubic hair

Female Sexual Response
The clitoris, vaginal mucosa, and breasts engorge with blood Activity of vestibular glands lubricates the vestibule and facilitates entry of the penis Orgasm – accompanied by muscle tension, increase in pulse rate and blood pressure, and rhythmical contractions of the uterus

Stages of Pregnancy and Development
Fertilization Embryonic development Fetal development Childbirth

Fertilization The oocyte is viable for 12 to 24 hours after ovulation
Sperm are viable for 1 to 7 days after ejaculation Sperm cells must make their way to the uterine tube for fertilization to be possible

Fertilization Sperm binds to the zona pellucida
Undergoes the acrosomal reaction Fusion of oocyte and sperm plasma membranes Cortical reaction - enzymes prevent any other sperm from binding to the egg Fertilization – chromosomes of male and female gametes join

Fertilization Membrane receptors on an oocyte pulls in the head of the first sperm cell to make contact The membrane of the oocyte does not permit a second sperm head to enter The oocyte then undergoes its second meiotic division Fertilization occurs when the genetic material of a sperm combines with that of an oocyte to form a zygote Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Zygote First cell of a new individual
The result of the fusion of DNA from sperm and egg The zygote begins rapid mitotic cell divisions The zygote stage is in the uterine tube, moving toward the uterus Blastocyst Inner cell Days 5-9: Blastocyst implants. Ovulation Day 1: Fertilization Days 2-4: Cell division takes place. Days 4-5: Blastocyst reaches uterus. Zygote Fallopian tube Egg Uterus Ovary 3 2 4 1 5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Embryo The zygote first undergoes division without growth
Enters the uterus at the 16-cell state early blastocyst The blastocyst floats free in the uterus temporarily Uterine secretions are used for nourishment Blastocyst Inner cell Days 5-9: Blastocyst implants. Ovulation Day 1: Fertilization Days 2-4: Cell division takes place. Days 4-5: Blastocyst reaches uterus. Zygote Fallopian tube Egg Uterus Ovary 3 2 4 1 5

Implantation of The Blastocyst
Blastocyst begins implantation about six days after conception Secretes human chorionic gonadotropin (hCG) to produce the corpus luteum to continue producing hormones Blastocyst Inner cell Days 5-9: Blastocyst implants. Ovulation Day 1: Fertilization Days 2-4: Cell division takes place. Days 4-5: Blastocyst reaches uterus. Zygote Fallopian tube Egg Uterus Ovary 3 2 4 1 5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Implantation Blastocyst consists of an inner cell mass and outer trophoblast Trophoblast forms two layers Cytotrophoblast – inner layer Syncytiotrophoblast – outer layer

Implantation Figure 24.24a–c

Development After Implantation
Chorionic villi (projections of the blastocyst) develop Cooperate with cells of the uterus to form the placenta The embryo is surrounded by the amnion (a fluid filled sac) An umbilical cord forms to attach the embryo to the placenta Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Functions of the Placenta
Forms a barrier between mother and embryo (blood is not exchanged) Delivers nutrients and oxygen and removes waste from embryonic blood Becomes an endocrine organ (produces hormones) and takes over for the corpus luteum Estrogen Progesterone Other hormones that maintain pregnancy

The Fetus (Beginning of the Ninth Week)
All organ systems are formed by the end of the eighth week Activities of the fetus are growth and organ specialization A stage of tremendous growth and change in appearance

Developmental Aspects: Genetic Sex Determination
Genetic sex is determined by the sex chromosomes each gamete contains There are two types of sex chromosomes: X and Y Females have two X chromosomes; males have one X and one Y Hence, all eggs have an X chromosome; half the sperm have an X, and the other half a Y A single gene on the Y chromosome, the SRY gene, initiates testes development and determines maleness

Inheritance of X and Y chromosomes
Sex Determination Inheritance of X and Y chromosomes Figure 26-2

Developmental Aspects
5th week – gonadal ridges form and paramesonephric (Müllerian) ducts form in females, mesonephric (Wolffian) ducts develop in males Shortly later, primordial germ cells develop and seed the developing gonads destined to become spermatogonia or oogonia Male structures begin development in the 7th week; female in the 8th week External genitalia, like gonads, arise from the same structures in both sexes

Sexual Differentiation
Bipotential tissues SRY gene Gonad Testis or ovary Wolffian duct Male Mullerian duct Female

Sexual Differentiation

Development of Internal Organs
Gonadal cortex becomes ovary in the absence of SRY protein. Absence of testosterone causes Wolffian duct to degenerate. SRY protein in a male embryo directs the medulla of the bipotential gonad to develop into testis. FEMALE MALE Bipotential gonad Müllerian duct Uterus (a) Development of internal organs Ovary Vagina Fallopian tube (from Müllerian duct) Testis Prostate Seminal vesicle Vas deferens Wolffian duct Epididymis Cloacal opening Kidney Anti-Müllerian hormone from testis causes the Müllerian ducts to degenerate. Absence of anti-Müllerian hormone allows the to become the fallopian tube, uterus, and upper part of the vagina. Bipotential stage: 6 weeks of fetal development The internal reproductive organs have the potential to develop into male or female structures. Testosterone from testis converts Wolffian duct into seminal vesicle, vas deferens, and epididymis. DHT controls prostate development. 10 WEEKS AT BIRTH 1 2 3 Figure 23-3a

Reproductive Organs at Birth

The Reproductive System

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